Projection Image Correction System and Projection Image Correction Method

1. A projection image correction system for correcting image data to be outputted to a projector, the system comprising: an image-taking section configured to take, via a lens, an image of a checkered sheet placed in a region where an image is projected from the projector; a correction section configured to correct lens-induced distortion of the taken checkered sheet image by using an internal parameter of the image-taking section; a checker intersection coordinate detection section configured to detect, with sub-pixel precision, checker intersection coordinates in the corrected checkered sheet image; a first transformation matrix calculation section configured to calculate a first projective transformation matrix for projective transformation of the detected checker intersection coordinates into checker intersection coordinates located at equal intervals in the region; a generation section configured to correct, when first positive images and first negative images of an 8-bit vertical Gray code pattern projected on the region from the projector are taken by the image-taking section, lens-induced distortion of the taken first positive images and first negative images by using the internal parameter of the image-taking section, and generate a first spatial code image whose code value changes in a lateral direction based on the corrected first positive images and first negative images, and to correct, when second positive images and second negative images of an 8-bit horizontal Gray code pattern projected on the region from the projector are taken by the image-taking section, lens-induced distortion of the taken second positive images and second negative images by using the internal parameter of the image-taking section, and generate a second spatial code image whose code value changes in a longitudinal direction based on the corrected second positive images and second negative images; a boundary coordinate acquisition section configured to obtain, with sub-pixel precision, an intersection of brightness profiles in the corrected first positive images and first negative images, and obtain, with sub-pixel precision, an intersection of brightness profiles in the corrected second positive images and second negative images, thus acquiring the obtained intersections as boundary coordinates; a boundary line intersection acquisition section configured to acquire, based on the acquired boundary coordinates, a boundary line connecting the boundary coordinates of the same code value in each of the first and second spatial code images, and combine the first and second spatial code images, thus acquiring coordinates of an intersection of the boundary line in the first spatial code image and the boundary line in the second spatial code image; a second transformation matrix calculation section configured to transform the acquired intersection coordinates by using the first projective transformation matrix, and calculate a second projective transformation matrix by which projective transformation is performed so that the transformed intersection coordinates are distributed over the entire region; and an image data correction section configured to transform, using the second projective transformation matrix, image data to be outputted to the projector, thus correcting the image data.

2. A non-transitory computer readable storage medium in which a program that allows a computer to function as the projection image correction system according to claim 1 is stored.

3. A projection image correction method for correcting image data to be outputted to a projector, the method comprising: preparing an image-taking section that includes a lens; taking, via the lens, an image of a checkered sheet placed in a region where an image is projected from the projector; correcting lens-induced distortion of the taken checkered sheet image by using an internal parameter of the image-taking section; detecting, with sub-pixel precision, checker intersection coordinates in the corrected checkered sheet image; calculating a first projective transformation matrix for projective transformation of the detected checker intersection coordinates into checker intersection coordinates located at equal intervals in the region; taking first positive images and first negative images of an 8-bit vertical Gray code pattern projected on the region from the projector by the image-taking section, correcting lens-induced distortion of the taken first positive images and first negative images by using the internal parameter of the image-taking section, and generating a first spatial code image whose code value changes in a lateral direction based on the corrected first positive images and first negative images; taking second positive images and second negative images of an 8-bit horizontal Gray code pattern projected on the region from the projector by the image-taking section, correcting lens-induced distortion of the taken second positive images and second negative images by using the internal parameter of the image-taking section, and generating a second spatial code image whose code value changes in a longitudinal direction based on the corrected second positive images and second negative images; obtaining, with sub-pixel precision, an intersection of brightness profiles in the corrected first positive images and first negative images, and obtaining, with sub-pixel precision, an intersection of brightness profiles in the corrected second positive images and second negative images, thus acquiring the obtained intersections as boundary coordinates; acquiring, based on the acquired boundary coordinates, a boundary line connecting the boundary coordinates of the same code value in each of the first and second spatial code images, and combining the first and second spatial code images, thus acquiring coordinates of an intersection of the boundary line in the first spatial code image and the boundary line in the second spatial code image; transforming the acquired intersection coordinates by using the first projective transformation matrix, and calculating a second projective transformation matrix by which projective transformation is performed so that the transformed intersection coordinates are distributed over the entire region; and transforming, using the second projective transformation matrix, image data to be outputted to the projector, thus correcting the image data.

4. A non-transitory computer readable storage medium in which a program that allows a computer to carry out the projection image correction method according to claim 3 is stored.